Re: New optimisations for long raw strings in C++ Mode.

[Eli Zaretskii]

> Date: Tue, 9 Aug 2022 16:05:40 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>, emacs-devel@gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > But opening the resulting file with "emacs -Q" and then doing a `M->'
> > now hangs Emacs, which it didn't use to do, I think?
> 
> If you do (setq long-line-threshold nil), M-> is fast.  Only when you
> omit it does Emacs hang.  Hmm.  It's meant to be the other way around,
> isn't it?  ;-)

Yes.  I'm guessing there's some additional bug there.

> What isn't so clever is that with a long line of y's, C-p, C-n, M-v, C-v
> are slower than inserting the long line.  The profiler on M-v indicated
> that scroll-down-command was taking 86% of the time.

If this is with long-line-threshold set to nil, then you have just
re-discovered the problematic performance of Emacs with very long
line, which long-line-threshold and the resulting selective narrowing
are designed to fix.

Btw, C-n/C-p don't call scroll-down-command, so I guess that was only
shown in the profile for M-v.